Oort cloud
The Oort cloud (/ˈɔːrt/ or /ˈʊərt/,[1] named after the Dutch astronomer Jan Oort), sometimes called the Öpik–Oort cloud,[2] is a theoretical cloud of predominantly icy planetesimals believed to surround the Sun to as far as somewhere between 50,000 and 200,000 AU (0.8 and 3.2 ly).[note 1][3] It is divided into two regions: a disc-shaped inner Oort cloud (or Hills cloud) and a spherical outer Oort cloud. Both regions lie beyond the heliosphere and in interstellar space.[3][4] The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud.